This invention relates to an exterior-mounted rear vision mirror for a vehicle.
An exterior-mounted rear vision mirror is generally acknowledged to be a very important aid to safety in driving. Its importance is likely to be greatly increased during rain when effectiveness of an internally-mounted rear vision mirror may be greatly diminished by poor visibility through the rear window; but in these conditions it is likely that rain drops or mist on an exterior-mounted mirror will greatly diminish its effectiveness.
An exterior-mounted mirror is also very likely to become soiled and obscured by dust and it may be so located that it is difficult or impossible to clean without stopping and leaving the vehicle.
It has been proposed, for example in Australian Patent Application No. 24507/71, to provide an exterior rear vision mirror rotatable about its axis within a housing open at the rear, the mirror being rotated either by the effect of air flow on vanes arranged about the mirror's periphery and extending outwardly of the housing, or by means of a small motor within the housing, so that rain drops will be thrown centrifugally from the mirror. However, it has been found that there is a very great loss of clarity in the reflection from a mirror which is rotated on an end of a motor drive shaft engaged in conventional bearings. If a driver looks, from at a 120mm diameter rotating mirror from a distance of 1 meter, at a reflection of a vehicle 15 meters behind the mirror, then if the mirror wobbles at its circumference by only 0.013mm to each side of vertical, then the image of the vehicle can appear to move by 0.75mm, and movement of this order is great enough to diminish very significantly the clarity of the reflected image, which will be too blurred to be acceptable as a safe rear vision mirror. The precision necessary to make an acceptable rotary rear vision mirror fixed perpendicularly to a motor drive shaft would be very difficult to achieve, and the product would be very costly.